Process of producing a natural gas substitute

Abstract

An improvement in the production of a natural gas substitute comprising at least about 80% of methane by volume by multi-stage methanation of a synthesis gas containing hydrogen and oxides of carbon over fixed-bed nickel-containing catalysts under a pressure of about 5 to 100 bars. The starting synthesis gas, preferably produced by oxygen and water gasification of coal, has about 8 to 25% by volume of methane on a dry basis. It is methanated in a first stage at an inlet temperature of about 230°-400° C. and an outlet temperature of about 550° to 750° C. and then in a second stage at about 230° to 500° C. The process is economical with respect to heat consumption and equipment cost.

What is claimed is: 
     
       1. In the production of a natural gas substitute comprising at least about 80% of methane by volume by multi-stage methanation of a synthesis gas containing hydrogen and oxides of carbon over fixed-bed nickel-containing catalysts under a pressure of about 5 to 100 bars, the improvement which comprises employing a synthesis gas having a methane content on a dry basis of about 8 to 25% by volume, effecting methanation in a first catalyst-containing stage wherein the gas has a temperature of about 230° to 400° C. at the entrance to the catalyst therein and a temperature of about 550° to 750° C. at the exit from the catalyst, said first stage comprising at least two adiabatically operating methanation reactors in sequence, each reactor being fed with part of the fresh synthesis gas, the first reactor being fed with a mixture of fresh synthesis gas and a recycled part of an effluent gas from one of the reactors, said part of the effluent gas being cooled and compressed, from the last reactor withdrawing a high-methane effluent gas and then effecting further methanation of the high-methane effluent gas in a second catalyst-containing stage at a temperature of about 230° to 500° C., thereby to produce a gas comprising at least about 80% of methane by volume, the catalyst in the reactors of said first stage by weight consisting essentially of about 25-50% of nickel, about 30% of high-alumina cement and at least about 5% of zirconium dioxide, the nickel being present as the compound Ni 5  MgAl 2  O 9  which compound is present in about 13 times the weight of zirconium dioxide. 
     
     
       2. A process according to claim 1, wherein the synthesis gas supplied to the first methanation stage has a methane content of about 10 to 20% by volume on a dry basis. 
     
     
       3. A process according to claim 1, wherein the synthesis gas is produced by gasification of coal, tar or heavy residue oil with oxygen and water vapor under superatmospheric pressure, cooling the resulting hot gas, and purifying such gas to remove catalyst poisons.